1. Field of the Invention
The present invention relates to a nickel oxide powder material for a solid oxide type fuel cell (SOFC) and production method thereof, and an anode material using it, and in more detail, relates to a nickel oxide powder material that can restrain cracking of electrode due to oxidation expansion and peeling from a electrolyte and thus can decrease deterioration of the power generation characteristics, even in the case that the anode is exposed to an oxidizing atmosphere, for example, caused by the disruption of the fuel supply at operating temperature, or the like when used as an anode material for a solid oxide type fuel cell and its efficient production method, and the anode material for the solid oxide type fuel cell using the nickel oxide powder material.
2. Description of the Prior Art
In recent years, a solid oxide type fuel cell has been expected as a new power generation system from the both standpoints of environment and energy.
Generally, a solid oxide type fuel cell is sometimes called a solid electrolyte type fuel cell and has a structure in which a cathode, a solid electrolyte and an anode are laminated in order. Usually, a solid electrolyte composed of, for example, nickel or nickel oxide and stabilized zirconia is used as an anode. In addition, porous LaMnO3 or the like is used as a cathode, and stabilized zirconia or the like is used as a solid electrolyte. It should be noted that, in such a solid oxide type fuel cell, oxygen taken in from the cathode side in the form of oxide ion, and hydrogen taken in from the anode side. Oxide ion through a solid electrolyte and hydrogen react electrochemically via solid electrolyte to generate electromotive force.
As a production method of the above solid oxide type fuel cell, in the case of a plate type, there is employed a method wherein firstly a cell-supporting member, which is generally an electrolyte or an anode, is prepared by tape molding or extrusion molding, and then tape molded product of other component member is laminated thereon, or a slurry is adhered on the cell-supporting member by coating, and then is sintered. Generally in this method, at least two of each component member such as the anode, the electrolyte and the cathode are sintered at the same time in order to simplify the production process and reduce the production cost. In the case of a tube type, a solid oxide type fuel cell is produced by applying each slurry of the materials constituting the electrode and the electrolyte to the tube supporting member followed by sintering.
Incidentally, an anode of a solid oxide type fuel cell is exposed to a reducing atmosphere by hydrogen and hydrocarbons during power generation, and the nickel oxide is reduced to metal nickel. Here, when the anode is exposed to an oxidizing atmosphere caused by the disruption of the fuel supply at operating temperature or an air leak caused by cell damage, the metal nickel is oxidized, and there has been a problem that the cracking of electrode due to oxidation expansion and peeling from a electrolyte happened and thus the characteristics such as power generation performance are deteriorated.
As a solution to the above-described problem, nickel oxide powder containing chromium oxide or manganese oxide is disclosed (for example, see Patent literature 1). Although, in these materials, an effect for restraining the shrinkage of an anode is confirmed, they do not seem to have a sufficient effect for restraining cracking, peeling and warping when the anode is exposed to an oxidizing atmosphere caused by the disruption of the fuel supply at operating temperature or the like.
It is also proposed that nickel or nickel oxide is coated with a small amount of an electrolyte by impregnating the porous base in a metal salt solution, drying and then sintering, after preparing a porous base by sintering once, in order to restrain cracking, peeling and warping when it is exposed to an oxidizing atmosphere caused by the disruption of the fuel supply at operating temperature or the like (for example, see Patent literature 2). This preparation method, however, is complicated and is not industrially effective.
Further, it is also reported that, when used as an anode material for a solid oxide type fuel cell, adjustment to a coarse microstructure of electrode has an effect for restraining cracking, peeling and warping when an anode is exposed to an oxidizing atmosphere caused by the disruption of the fuel supply at operating temperature or the like (for example, see Non-patent literature 1), however, the coarse micro structure is not preferable because it sacrifices a reaction interface (three phase boundary: TBP) and causes deterioration of the power generation characteristics.
Under the above situations, a nickel oxide powder material has been desired that can restrain cracking of anode due to oxidation expansion and peeling from a solid electrolyte and thus can decrease deterioration of the power generation characteristics in the case that the anode is exposed to an oxidizing atmosphere caused by the disruption of the fuel supply at operating temperature or the like without impairing the performance as a final fuel cell system when used as an anode material in producing a solid oxide type fuel cell.    Patent literature 1: WO/2007/020863 (page 1, Page 2)    Patent literature 2: JP-A-8-55625 (page 1, Page 2)    Non-patent literature: “solid state ionics”, (Holland), 2005, No. 176, p. 847-859